Meningiomas

See related articles on Space-occupying Lesions, Brain Tumours in Children and Brain Tumours in Adults.

Meningiomas are mostly benign tumours which arise from the dura mater and are usually slow growing.

• They are the commonest benign intracranial tumours and account for up to 13-26% of primary intracranial tumours.¹
• Incidence 6 per 100,000 - highest after 50 years of age.¹
• Female to male ratio of 2:1.
• 2-3% of the population have asymptomatic meningiomas.
• 8% have multiple meningiomas.

• Aetiology is not known and most cases are sporadic.²
• Some are increased in the presence of certain genetic disorders e.g. loss of chromosome 22 and presence of neurofibromatosis type 2.^2,3
• Other risk factors include cranial irradiation (as in tinea capitis), head injury and breast cancer (although causality not determined).¹

• Skull vault
• Skull base e.g. sphenoid wing and petrous ridge
• Sites of dural reflection e.g. falx cerebri and tentorium cerebelli
• Optic-nerve sheath
• Choroid plexus
• Spine (rarely)
• Outside the craniospinal axis (very rarely) e.g. ear, temporal bone and foot

Macroscopically

• Meningiomas usually form well-circumscribed lesions
• Rarely, they can be more diffuse e.g. when they grow next to the sphenoid ridge and are called "meningioma en plaque"

• Neoplastic arachnoidal cells
• Cellular whorls are characteristic
• Intra-nuclear pseudo-inclusions
• Anaplastic subtypes have foci of necrosis

This can be in various ways e.g. site of origin, encroachment of surrounding tissues and histological grading. The commonest system used is the WHO classification.

• Proliferation markers provide information on likelihood of recurrence.
• For example, MIB-1 and Ki67 are found in higher levels of tumours that are likely to recur.^1,4
• However, further work is needed to clarify the role of proliferation markers and prognosis.
• Meningiomas can also express progesterone receptors.⁵
• Higher levels of progesterone receptors have been reported to be associated with a lower frequency of recurrence and a better prognosis.
• More than 70% of meningiomas express somatostatin receptors which can be used with radiological imaging, especially when looking for local recurrence.^1,6

This is as a space occupying lesion and includes:

• Seizures - focal or generalised are common with meningiomas
• Raised intracranial pressure effects e.g. obstructive hydrocephalus with headache
• Neuropsychological effects e.g. change in personality and disinhibition in frontal lesions
• Neurological features e.g. cranial nerve palsies depending on location of meningioma or language dysfunction
• Transient ischaemic attack and intracranial haemorrhage may also be seen

This is as for other space occupying lesions. It is important to remember that meningiomas can be discovered incidentally when patients are investigated for other conditions. Other lesions which may also affect the dura mater include:

• Metastases from lymphoma and adenocarcinoma
• Inflammatory disorders e.g. sarcoidosis
• Infections e.g. tuberculosis

Imaging - MRI is superior to CT scanning as it shows the dural origin. Meningiomas are well-defined, extra-axial lesions. They may show central cystic degeneration and oedema of nearby white matter.

Management will depend on:

• Asymptomatic or symptomatic
• Age of patient
• Site of tumour
• Size of tumour

For example, an elderly patient with multiple co-morbidities who is discovered to incidentally have a small, asymptomatic meningioma can be managed conservatively. This usually consists of yearly MRIs and at 3 years if nothing new has developed patients can be followed up clinically.¹

Endovascular embolisation

• This involves embolisation of the blood supply to the meningioma e.g. coil or glue applied endovascularly to the meningeal artery.⁷
• This is usually performed before surgical removal as it reduces the amount of blood loss.⁸
• It has also been performed as the primary therapy in those unsuitable for surgery.
• Embolisation usually causes necrosis of the meningioma which can cause some histological doubt when specimens are examined post-operatively.¹

Surgical removal

• The tumour and its dural base are removed.
• Total excision is the aim but this is not always possible e.g. close neural tissue or en plaque meningiomas.
• Surgery may be complicated by invasion into local structures e.g. parasagittal tumours invading into the cerebral dural sinus.

Radiotherapy

• Radiotherapy is used in the following:
  • Incomplete resection
  • Following recurrence of meningioma
  • Meningioma has atypia or anaplasia at histology
• In these clinical scenarios the use of radiotherapy is associated with a better outcome. For example, in one study stereotactic radiosurgery was associated with better tumour control (approximately 10%) and fewer complications.⁹ However, a recent paper has shed some doubt on how useful radiotherapy is in meningiomas.¹⁰
• Stereotactic application of radiotherapy has further benefits compared with traditional radiotherapy. This includes less damage to undiseased tissue and better 5-year control rates.^1,11,12
• Radiotherapy is successful and may be used as the primary therapy for tumours especially inaccessible meningiomas e.g. optic nerve lesions.¹

Chemotherapy and molecular agents

• Some patients will not respond to surgery and radiotherapy.
• Chemotherapeutic regimens involving hydroxyurea have been used but with little success.^13,14
• More novel molecular targets are being researched.^15,16

Atypical and anaplastic types of meningiomas can rarely metastasise. The five-year survival for typical meningiomas is more than 80%, however this falls to below 60% in malignant and atypical meningiomas.¹⁴